Temperatures at 4 p.m. Thursday

Over the past five days, June heat unprecedented in modern times has torched parts of the Rockies, Plains, and mid-South. The heart of this scorching air mass is spilling towards the Tennessee Valley and Southeast, where it will settle through the weekend.

Heat advisories and excessive heat warnings are in effect in at least 21 states east of the Rockies Friday.

NAM model predicts a high of 102 in Washington, D.C. Friday

On Friday, the high temperature in D.C. and Baltimore should reach around 100 degrees. In D.C., one model predicts a high of 102, which would tie the hottest temperature ever recorded in June (reached last year and in 1874). Factoring in humidity, it will feel close to 105 degrees.

Record high temperatures set Wednesday (NOAA)

Today, Indianapolis touched 103, breaking both its daily and monthly heat record.

Friday through the weekend, the worst of the heat promises to stretch from western Kentucky to the Carolinas where the Weather Channel projects all-time record highs will be threatened.

Weather.com indicates a host of cities in the Southeast and Tennesse Valley could see high temperatures challenging all-time records. (Weather.com)

For Washington, D.C. and Baltimore, a protracted heat wave is likely, with highs of 95 or better possible through July 4, at least.

The heat brings with it all kinds of unwelcome consequences.

It has stoked the devastating wildfires in the Rockies and spread smoke over a large part of the U.S., according to University of Maryland’s Smog Blog. The smoke and elevated ozone levels triggered by the heat are compromosing air quality in many areas.

Link: Air quality maps and forecasts (AirNow)

Large parts of the Tennessee and Ohio Valley have air quality unhealthy for sensitive groups. For much of the East Coast, air quality is moderate and may worsen in the coming days.

Heat stress and heat exhaustion are another concern. The National Weather Service has cautioned the heat will be “debilitating” and is urging heat wave preparedness.

Links: Capital Weather Gang’s Heat wave and hot weather guide and Department of Labor urges heat safety for outdoor workers

Climate Central’s Andrew Freedman also notes: “[the heat] is prompting concerns about the U.S. corn crop, which is particularly sensitive to dry and hot conditions at this time of year”.